Hydrogen is used extensively in petroleum refining to upgrade the quality of various hydrocarbon products. One example is the desulfurization of gasoline and diesel fuels to remove sulfur which would, otherwise, be emitted as SO.sub.x in the combustion engine exhaust. Currently, the main source of hydrogen in a typical refinery is the process for the catalytic reforming of naphtha. However, with the arrival of the clean fuel regulations, which will require a significant reduction in gasoline aromatic levels, reformer severity will need to be reduced, and as a result, hydrogen production will be reduced. Compounding the problem is a related clean fuel requirement that the olefin and sulfur levels of gasoline be reduced, which will tend to increase the demand for hydrogen. The anticipated hydrogen deficiency can be off-set through outside purchases or construction of on-site hydrogen production plants. Both are costly options, with the outside purchase option also having the added disadvantage of a built-in dependence on outside suppliers.
In anticipation of the hydrogen deficiency problem, alternative approaches for producing hydrogen directly from refinery hydrocarbon streams, particularly waste streams, are being sought. One promising pathway is the production of hydrogen from hydrogen sulfide, an abundant byproduct of a number of refinery operations, e.g., catalytic and thermal cracking and hydrodesulfurization. Commonly, following recovery and purification of the H.sub.2 S stream by amine scrubbing, the H.sub.2 S is fed to a Claus plant where it is converted to water and elemental sulfur in a two step process. The first step in the process involves the combustion of part of the H.sub.2 S to form water and SO.sub.2. The SO.sub.2 reacts further with the balance of the H.sub.2 S in the second step to produce elemental sulfur and more water. The energy value of the hydrogen is lost in the process due to the formation of water. Other examples of processing options for H.sub.2 S include chelation, and liquid-redox systems (e.g. Stretford).
If for simplicity, it is assumed that all of the sulfur generated in a refinery is H.sub.2 S based, hydrogen production potential from H.sub.2 S for a typical high conversion 200,000 BPD refinery is estimated below in Table 1.
TABLE 1 ______________________________________ H.sub.2 Potential, Crude Gravity, API Crude Sulfur, wt. % MMSCFD ______________________________________ 22.5 3.5 20 30.0 2.0 10 35.0 0.5 2 ______________________________________
A considerable body of literature exists on the production of hydrogen from hydrogen sulfide. The methods of production include direct dissociation via thermal, electrolytic, and photochemical methods, high energy dissociation (e.g. microwave), as well as numerous catalytic methods, including those involving reaction with CO and CO.sub.2.